1. Field of the Invention
The present invention relates to a magnetic head and more particularly to a magnetic head of the type in which a core half on the side of a recording medium incoming side and a core half on the side of a recording medium outgoing side are disposed in opposing relation through a magnetic gap which is used for magnetic recording.
2. Description of the Prior Art
The data packaging density of magnetic recordings has recently been remarkably increased. As a result video tape recorders (VTRs) using magnetic tape 8 mm in width and digital audio tape recorders (DATs) or the like have been developed, along with the development of magnetic heads and recording media which have high data packaging density.
There are known flexible disk drives (FDDs) which use flexible magnetic recording media (flexible disks), as the magnetic recording apparatuses capable of attaining a high data packaging density. In the FDDs, it is known to increase the data packaging density by a method which increases not only the line recording density but also the track density. Table 1 shows the maximum line recording density, the track density and the track pitch of FDDs which use flexible disks having capacities (unformatted) of 1 megabyte (MB), 2 MB, MB, 12.5 MB and 16 MB.
TABLE 1 ______________________________________ Line recording density track density track pitch ______________________________________ 1 MB 8.7 KBPI 135 TPI 187.5 .mu.m 2 MB 17.4 135 187.5 4 MB 34.9 135 187.5 12.5 MB 36.0 406 62.5 16 MB 35.0 540 47.0 ______________________________________
In Table 1, KBPI represents the number of kilobytes per inch and TPI represents the number of tracks per inch.
As is clear from Table 1, the increase in line recording density and track density greatly increases the recording capacity of FDDs.
FIG. 1 is a view used to explain a recording system employing a magnetic head used in an FDD with a capacity ranging from 1 to 2 MB, a data track being projected upon the contact surface with a recording medium of the magnetic head. This system is called the tunnel erasure system. As shown in FIG. 1, after the recording in a recording-reproducing gap or R/W gap 1, both sides of the recorded loci are erased by two erasing heads so that the track 3 on which data are recorded remains. Here, the recording medium moves in the direction indicated by the arrow 4.
Even when the size of the R/W gap 1 varies and the position of the track deviates, both side bands are erased by the two erasing gaps 2 so that data on both side bands is positively erased. Therefore this method is used in FDDs (mainly 1 MB-2 MB) with a track density on the order of 200 TPI.
However, in the case of FDDs with capacities ranging from 12.5 MB to 16 MB and a high track density ranging from 406 TPI to 540 TPI, as shown in FIG. 2, after positioning of the head by previously recorded servo signals 5a and 5b, the data is read out from or written in the track 3 by the R/W gap. That is, the head is located at the position at which the reproduced outputs of the servo signals 5a and 5b coincide.
Because the position of the head relative to the track is determined in response to the servo signals 5a and 5b and the track pitch becomes narrower, in general, the FDDs do not use the magnetic head of the tunnel erasing method shown in FIG. 1, but use a magnetic head with only an R/W gap.
However, even when a magnetic head having only an R/W gap as shown in FIG. 2 is used, errors sometimes occur in the width of the track and the deviation of the position of the head relative to the servo signals 5a and 5b. In this case, as shown in FIG. 3, when new data is recorded on the track 3 on which data has been already recorded, if deviation 7 of the position of the track occurs and a track 6 on which new data has been recorded by the R/W gap 1 is formed, the old data 8 which has not been erased remains.
Especially, in the case of FDDs, the recording medium is not fixed to the apparatus. And in many cases the recording medium on which the data has been recorded and read out are used by other FDDs. That is, so-called interchangeability is needed. However, when the data which has not been erased remains, the remaining data is also read out together with the readout of the newly recorded data so that errors are contained in the reproduced data. Especially, in the case of FDDs, the error rate in the data processing is strictly limited from 10-9 to 10-12. Therefore the data which has not been completely erased becomes a very serious problem.